Díaz was a solid catcher for the next two seasons with Philadelphia, though always an erratic hitter. He also started for Cincinnati later in the decade, making another All-Star team in 1987. He made his only post-season appearance with the 1983 Phillies, going 5 for 15 in a losing cause in the World Series against the Baltimore Orioles.

Díaz is best remembered for cult accomplishments, including throwing out Robby Thompson on four stolen base attempts (June 27, 1986) and hitting a 2-out walk-off grand slam to turn a 9-6 deficit into a 10-9 Phillies win over the New York Mets on April 13, 1983. Diaz held the Venezuelan League home run record for over 30 years, the first player to do so. He drilled 20 homers for the 1979-1980 Leones del Caracas to break Bobby Darwin's 7-year-old mark of 19. He was the first Venezuelan to hold the record since Vidal López had a share of it with 9 in 1949-1950; in 1950-1951, it transferred to American or Cuban hands until Bo came along. Alex Cabrera finally topped Bo's mark in 2013-2014.

Díaz died in 1990 when a satellite dish that he was installing at his Caracas home fell and crushed him.